DESCRIPTION (Verbatim from Applicant's Abstract): The objective of this proposal is to develop the technique of Electrical Impedance Tomography (EIT) imaged cryosurgery. An E1T image is acquired by: a) injecting small, sinusoidal electrical currents into the body, b) measuring the resulting voltages on the surface of the body through an electrode array and c) producing an impedance image from the voltage data, using a reconstruction algorithm. EIT offers high sensitivity, fast image acquisition, and virtually no dosage concerns in a comparatively inexpensive technology. E1T has the potential for becoming an important imaging modality for monitoring minimally invasive surgery. Cryosurgery is a minimally invasive surgical technique in which undesirable tissues are frozen and then left in situ to be absorbed. It can be highly effective in treatment of solid tumors. The application of cryosurgery to deep body tissues is prevented by the inability to observe the shape of the frozen region during treatment. Because freezing modifies the electrical properties of the tissue, EIT could image the freezing of tissue inside the body during cryosurgery. This is a technology driven proposal for the development of an Electrical Impedance Tomography (EIT) system for imaging the process of freezing during cryosurgery. To achieve this goal and verify this hypothesis we will pursue the following specific aims: 1) Determine sensitivity of EIT imaged cryosurgery by solving a mathematical model for the potential that develops in tissue from electrical currents injected into the tissue. The study will examine the effect of electrode location, electrode number, injected current frequency and amplitude, tissue type, and frozen lesion geometry, 2) Develop the hardware for ISll-imaged cryosurgery, 3) Develop and verify the software for EIT-imaged cryosurgery. We will design an inverse mathematical technique to reconstruct an image of the frozen region from the externally measured currents and potentials, 4) Test the hardware and the software in vivo in animal liver, and skin cryosurgery. Completion of the project will establish EIT as effective for imaging minimally invasive surgical procedures in general and cryosurgery, in particular.